1. Field of the Invention
The invention relates generally to navigation systems and, more particularly, to navigation systems that incorporate inertial and GNSS subsystems.
2. Background Information
Inertial/GNSS receivers, such as the receivers described in U.S. Pat. Nos. 6,721,657 and 7,193,559, which are assigned to a common assignee and incorporated herein by reference, work well to provide accurate and uninterrupted navigation information, even in environments in which sufficient numbers of GNSS satellites are not continuously in view. As is described in the patents, the inertial/GNSS receivers utilize inertial measurements to fill-in whenever the GNSS subsystem does not receive GNSS satellite signals from a sufficient number of GNSS satellites to determine position. Further, the inertial/GNSS receivers combine, in real time, information from the GNSS and inertial subsystems to aid in signal re-acquisition and in the resolution of associated carrier ambiguities when a sufficient number of GNSS satellite signals are again available.
At start-up, the inertial/GNSS receivers must initialize the inertial and the GNSS subsystems before the inertial/GNSS receiver can operate in steady state navigation mode. The more quickly and accurately the inertial/GNSS receiver can complete the initialization, the faster the inertial/GNSS receivers can provide the accurate and uninterrupted navigation information to a user. Further, the inertial and GNSS subsystems must typically experience dynamic motion after or during start-up in order for the inertial/GNSS receivers to calculate the navigation information utilizing a combination of inertial measurements, GNSS observables, and GNSS position and covariance information.
We have developed a navigation system that speeds-up the initialization process for the inertial and GNSS subsystems without adversely affecting accuracy. Further, the navigation system enables the inertial and GNSS subsystems to utilize a combination of inertial measurements, GNSS and other observables, and GNSS position and covariance information to determine the navigation information after the initialization is complete, regardless of whether or not the inertial and GNSS subsystems have experienced dynamic motion.